Sleep Problems - What is wrong?

Hi, I'm 16 and I've been having trouble sleeping for years, but lately its gotten terrible. Take last night for instance, I went to bed at around 12, but I didn't fall asleep, At All. At around 5 i decided i had laid there enough and went to sit on the shed behind my house for a hour. My mom was not happy when she found out that i hadn't slept at all. I don't know at all what has been causing this, but its been happening for years, It used to be only a half hour or so but now its gotten to be 4 or more hours some nights that I lay there without falling asleep. Does anyone know if this is Insomnia, or what may be wrong, and what I can do to right it? Its really becoming a hindrance to me and my parents.